Selecting the right stepper motor requires precise calculations to ensure optimal performance. When making a selection, factors such as flange size, number of phases, motor length, shaft length, and the number of output wires must be carefully considered. Additionally, it’s essential to calculate torque and current requirements and verify compatibility with the matching driver.
1. Choosing the Torque for a Stepper Motor
The holding torque of a stepper motor is analogous to the “power” in traditional motors, though there are fundamental differences. The physical structure of stepper motors is distinct from that of AC or DC motors, as the output power of a stepper motor is variable. Selection is typically based on the required torque, i.e., the force needed to drive a load.
- For torque requirements below 0.6 N·m, motors with frame sizes of 28 mm, 35 mm, or 42 mm are suitable.
- For torque requirements above 0.6 N·m, 57 mm motors are generally more appropriate.
- For higher torque needs, such as several N·m or more, motors with frame sizes of 86 mm, 110 mm, or 130 mm are recommended.
Common Stepper Motor Sizes:
20 mm | 28 mm | 35 mm | 42 mm | 57 mm | 60 mm | 86 mm | 110 mm | 130 mm
2. Selecting the Number of Phases
The number of phases is an often-overlooked factor when selecting stepper motors. However, it significantly impacts performance. Different phase configurations (commonly two-phase, three-phase, or five-phase) provide varying levels of precision and stability.
- A higher number of phases results in smaller step angles and reduced vibration during operation.
- Two-phase motors are widely used in most applications.
- Three-phase motors are preferable for high-speed, high-torque applications.
3. Selecting the Motor Speed
The speed of a stepper motor requires careful consideration because the output torque is inversely proportional to the rotational speed.
- At low speeds (several hundred RPM or less), stepper motors produce higher output torque.
- At high speeds (1,000–9,000 RPM), the torque output decreases significantly.
- For applications requiring high-speed operation, motors with lower coil resistance and inductance are recommended.
- For low-speed, high-torque requirements, motors with higher inductance (e.g., 10–50 mH) and higher resistance are more suitable.
4. Selecting the No-Load Start Frequency
The no-load start frequency, commonly referred to as the “start frequency,” is a critical parameter for stepper motors.
- Applications that require frequent instantaneous starts and stops, especially at speeds around 1,000 RPM or higher, often require an “accelerated start.”
- For direct high-speed starts, reactive or permanent magnet stepper motors with higher start frequencies are ideal.
By carefully analyzing these factors, you can select a stepper motor that meets your specific application requirements while ensuring reliable and efficient operation.
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